It is known that chelating agents such as ethylenediaminetetraacetic acid dianhydride (EDTA-dianhydride) or diethylenetriaminepentaacetic acid dianhydride (DTPA dianhydride) can be directly coupled to biological substrates to form conjugates which can be labeled with radionuclides used in in vivo imaging applications. However, EDTA and DTPA conjugates have shown limitations as to the variety of radionuclides that can be chelated, and as to their in vivo stabilities.
Accordingly, one or more of the following objects will be achieved by the practice of the present invention. It is an object of this invention to provide 8-hydroxyquinoline derivatives which are capable of forming chelates with a variety of radionuclides. Another object of this invention is to provide bifunctional 8-hydroxyquinoline derivatives which can be readily coupled to biological substrates, and the conjugates so formed can then be labeled with radionuclides which are suitable for diagnosis and therapy. It is a further object of the invention to provide radioisotope labeled compounds possessing superior in vivo stabilities.